We introduce an $\mathrm{SU}(N)$ symmetric two-dimensional quantum spin model, the $X\text{−}Q$ model, which hosts a ground state transition between Néel antiferromagnetic and spontaneously dimerized states. The $Q$ terms are products of two adjacent singlet projectors on nearest-neighbor sites, as in the often studied $J\text{−}Q$ model (where $J$ is the Heisenberg exchange), while the $X$ terms are products of two permutation operators on second-neighbor sites. Quantum Monte Carlo simulations reveal close proximity to a deconfined quantum critical point for $N=2$, as in the $J\text{−}Q$ model. However, for $N>2$ the transition becomes strongly first order, contrary to conventional expectations that increasing $N$ should weaken discontinuities. We attribute this behavior to the inability of the $X$ term to induce U(1) fluctuations of the dimer pattern, while those from the $Q$ term are suppressed by $1/N$. These results provide insights into the interactions that support deconfined criticality.

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• Antiferromagnetism
• Quantum spin liquid
• Heisenberg model
• Quantum Monte Carlo